1. Technical Field
The present invention relates to liquid ejecting apparatuses such as ink jet printers, and particularly relates to a liquid ejecting apparatus capable of controlling the ejection of a liquid by applying an ejection driving pulse to a pressurizing unit.
2. Related Art
A liquid ejecting apparatus is an apparatus that is provided with a liquid ejecting head capable of ejecting a liquid from a nozzle, and that ejects various types of liquids from this liquid ejecting head. An image recording apparatus such as an ink jet printer (called simply a “printer” hereinafter) that is provided with an ink jet recording head (called simply a “recording head” hereinafter) as its liquid ejecting head and that records images and so on by causing ink in liquid form to be ejected from a nozzle in the recording head and land upon a recording medium such as a recording sheet (an ejection target) can be given as a representative example of such a liquid ejecting apparatus. Meanwhile, in addition to such image recording apparatuses, liquid ejecting apparatuses are recently being applied in various types of manufacturing apparatuses, such as apparatuses for manufacturing color filters for liquid crystal displays.
For example, the stated printers include printers that have a nozzle row (a type of nozzle group) configured by arranging multiple nozzles in a row, the printers being configured so that an ejection driving pulse is applied to a pressurizing unit (for example, a piezoelectric element, a heat generating element, or the like) in order to drive the unit, changing the pressure of the liquid within a pressure chamber, and employing the pressure change to eject the liquid from the nozzles, which communicate with the pressure chamber. To be more specific, a driving signal including one or more ejection driving pulses within a unit cycle, which is the unit by which the driving signal repeats (specifically, a cycle defined by a timing signal such as a LAT signal or the like), is generated, a number of ink ejections equivalent to the number of ejection driving pulses applied to the pressurizing unit are instigated, and dots are formed by causing the ink to land upon that recording medium. Images or the like are formed upon the recording medium by collections of multiple dots. According to this configuration, the size of pixels, which are the units of which the images or the like are formed, can be adjusted by increasing/decreasing the number of ink ejections within the unit cycle. In other words, multi-tone recording can be carried out by increasing/decreasing the number of inks.
However, in the case where, for example, high-speed printing is carried out on a roll of paper or the like serving as the recording medium at a printing speed in excess of 100 m per minute, the relative speed between the recording head and the recording medium increases, and there is thus a risk that multiple inks ejected from the same nozzle during the unit cycle will land in locations that are skewed relative to each other in the stated relative movement direction. This skew in the landing positions of dots has been a cause of drops in the quality of images and the like. Accordingly, to enable such high-speed printing, a scheme has been proposed in which, in a configuration that ejects ink (ink droplets) twice in succession from the same nozzle within a unit cycle, the flight speed of the second ejected ink droplet is set to be faster than the flight speed of the first ejected ink droplet, thus causing the ink droplets to combine in flight, resulting in the ink droplets landing upon the recording medium as a single ink droplet (see, for example, Patent Document JP-A-2003-175599).
Incidentally, with this type of printer, when ink is ejected simultaneously from multiple nozzles that are adjacent to each other in a nozzle row, vibrations or the like caused by the aforementioned pressure fluctuations, driving of the pressurizing unit, and so on among the nozzles mutually affect the respective nozzles, and this has posed a problem in that so-called crosstalk, in which the ejection properties such as the flight speed, amount (mass or volume), and so on of the ejected ink has occurred between cases where ink is ejected singly from one nozzle and cases where ink is ejected simultaneously from multiple adjacent nozzles. There is a trend, particularly in recent years, for nozzles to be formed at high densities in order to meet demand for improvements in the image quality of recorded images. When nozzles are disposed at high densities, there has been a problem in that crosstalk occurs with ease when inks are ejected simultaneously from adjacent nozzles. The influence of crosstalk can be suppressed by reducing the flight speed of the ink; however, it should be noted that this poses a problem in that the flight speed, ink amount (mass or volume), and so on that are required for the aforementioned high-speed printing cannot be ensured.
FIGS. 6A through 6C are diagrams illustrating the influence of crosstalk when ink is ejected in a past printer, and are, to be more specific, diagrams illustrating conditions arising when ink is ejected from nozzles of which a nozzle row is configured toward a recording medium as viewed from the direction perpendicular to the flight direction of the ink (that is, the lateral direction). Note that in FIGS. 6A through 6C, the straight lines in the upper areas indicate the nozzle surface of the recording head, whereas the straight lines in the lower areas indicate the recording surface (printing surface) of the recording medium. Furthermore, FIGS. 6A through 6C illustrate the flight conditions of ink droplets in the case where, of nozzles #1 through #15, ink is ejected from nozzles #1 through #6 and #10 through #15, whereas ink is not ejected from nozzles #7 through #9 (that is, six nozzles on and three nozzles off). Note that the nozzles #1 through #6 and the nozzles #10 through #15 configure individual respective nozzle groups (adjacent nozzle groups).
FIG. 6A illustrates the flight conditions of ink droplets ejected by the leading ejection driving pulse in the case where ink is ejected using two ejection driving pulses within the unit cycle.
In a case such as this, where ink is ejected simultaneously from multiple adjacent nozzles, vibrations and the like occurring at that time exert mutual influence among the nozzles that are adjacent to each other, and thus there is a trend for the flight speed of the ink to drop in nozzles that are located closer to the central portions of the adjacent nozzle groups and the flight speed of ink to increase in nozzles that are located closer to the outer end portions of the adjacent nozzle groups. Accordingly, observing the respective ink droplets that are ejected from these nozzle groups shows that the inks travel in a state in which the ink droplets toward the central portion are closer to the nozzle surface and the ink droplets toward the outer end portions are closer to the recording medium, or in other words, a state in which the ink droplets form an arched shape whose central portion bulges upward (toward the nozzle surface). The trend toward the stated arched shape is particularly strong as the flight speed of the ink droplets is increased to comply with applications such as high-speed printing. Meanwhile, as shown in FIG. 6B, the inks also travel in a state that is essentially an arched shape whose central portion bulges upward even in the case where ink is ejected simultaneously from multiple adjacent nozzles as a result of the second ejection driving pulse in the unit cycle. Accordingly, as shown in FIG. 6C, even if the leading ink droplets and the following ink droplets combine during flight, observing the post-combination ink droplets shows that the inks travel in a state that is essentially an arched shape whose central portion bulges upward.
Here, ink droplets that have a higher flight speed land upon the recording medium in a shorter amount of time, and the time it takes for an ink droplet to land upon the recording medium is longer, the slower the flight speed is. In a configuration in which printing is carried out while the recording head and the recording medium move relative to each other, the locations at which the inks land upon the recording medium differ depending on the flight speeds of the ink. Accordingly, groups of dots formed when the inks land upon the recording medium are curved into an arched shape when viewed from above. This has resulted in a problem in that the quality of the recorded image or the like has decreased.